Single crystal diamond

ABSTRACT

A method of producing a large area plate of single crystal diamond from CVD diamond grown on a substrate substantially free of surface defects by chemical vapour deposition (CVD). The homoepitaxial CVD grown diamond and the substrate are severed transverse to the surface of the substrate on which diamond growth took place to produce the large area plate of single crystal CVD diamond.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.11/743,680 filed on May 3, 2007, which is a continuation application ofU.S. patent application Ser. No. 10/665,550, filed Sep. 22, 2003, theentire contents of all of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates to single crystal diamond.

Diamond offers a range of unique properties, including opticaltransmission, thermal conductivity, stiffness, wear resistance and itselectronic properties. Whilst many of the mechanical properties ofdiamond can be realised in more than one type of diamond, otherproperties are very sensitive to the type of diamond used. For example,for the best electronic properties CVD single crystal diamond isimportant, often outperforming polycrystalline CVD diamond, HPHT diamondand natural diamond.

In many applications of diamond the limited lateral dimensions of thediamond available is a substantial limitation. Polycrystalline CVDdiamond layers have substantially removed this problem for applicationswhere the polycrystalline structure is suitable for the application, butin many applications polycrystalline diamond is unsuitable.

Whilst natural and HPHT diamond may not be suitable for someapplications, they are used as substrates on which to grow CVD diamond.Although substrates can have a variety of crystallographic orientation,the largest and most suitable substrate orientation which can beproduced for growth of high quality CVD diamond is generally (001).Throughout this specification, the Miller indices {hkl}, defining aplane based on the axes x,y,z will be written assuming that the zdirection is that normal to the substrate surface and parallel to thegrowth direction. The axes x,y are then within the plane of thesubstrate, and are generally equivalent by symmetry but distinct from zbecause of the growth direction.

Large natural single crystal diamond is extremely rare and expensive,and large natural diamond substrate plates suitable for CVD diamondgrowth have not been demonstrated because of the associated very higheconomic risk in their fabrication and use. Natural diamond is oftenstrained and defective, particularly so in larger substrate plates, andthis causes twins and other problems in the CVD overgrowth or fractureduring synthesis. In addition, dislocations which are prevalent in thenatural diamond substrate are replicated in the CVD layer, alsodegrading its electronic properties.

HPHT synthetic diamond is also limited in size, and generally is ofpoorer quality in the larger stones, with inclusions being a majorproblem. Larger plates fabricated from synthetic diamonds generallyexhibit missing corners so that edge facets other than {100} (such as{110}) are present, or they are included or strained. During synthesisfurther facets are formed, such as the {111} which lies between the(001) top face and the {110} side facets (see FIG. 1 of the accompanyingdrawings). In recent years significant effort has been directed atsynthesising HPHT diamond of high quality for applications such asmonochromators, and some progress has been reported, but the size ofHPHT plates suitable for substrates remains limited.

{111} faces in particular are known generally to form twins during CVDsynthesis of thick layers, limiting the area of perfect single crystalgrowth and often leading to degradation and even fracture duringsynthesis, further exacerbated by thermal stresses resulting from thegrowth temperature. Twinning on the {111} particularly interferes withincreasing the size of the largest plate which can be fabricated with a(001) major face and bounded by {100} side faces.

Routinely available (001) substrates range up to about 7 mm square whenbounded by {100} edges, and up to about 8.5 mm across the major facewhen bounded by {100} and {110} edges.

CVD homoepitaxial synthesis of diamond involves growing CVD epitaxiallyon an existing diamond plate and is well described in the literature.This is of course still limited by the availability of existing diamondplates. In order to achieve larger areas, the focus has been to growlaterally as well, increasing the overall area of the overgrown plate.Such a method is described in EP 0 879 904.

An alternative to homoepitaxial growth is heteroepitaxial growth, wherea non-diamond substrate is grown on with an epitaxial relationship. Inall reported cases however, the product of this process is quitedistinct from homoepitaxial growth, with low angle boundaries betweenhighly oriented but not exactly oriented domains. These boundariesseverely degrade the properties of the diamond.

Homoepitaxial diamond growth to enlarge the area of a CVD plate presentsmany difficulties.

If it was possible to achieve ideal homoepitaxial growth on a diamondplate, the growth which would be achieved is substantially thatillustrated by FIGS. 1 and 2 of the accompanying drawings. The growthmorphology illustrated assumes that there is no competingpolycrystalline diamond growth. However, in reality, there is generallycompetition from polycrystalline growth, growing up from the surface onwhich the diamond substrate plate is mounted. This is illustrated byFIG. 3 of the accompanying drawings.

Referring to FIG. 3, a diamond substrate plate 10 is provided mounted ona surface 12. Example materials for surface 12 include molybdenum,tungsten, silicon and silicon carbide. During CVD diamond growth, singlecrystal diamond growth will occur on the (001) face 14 and on the sidesurfaces, two of which 16 are shown. The side surfaces 16 are {010}surfaces. Growth will also occur on and extend outwards from the cornersand vertices 18 of the plate. All such growth will be homoepitaxialsingle crystal growth. The growth on each of the faces present on thesubstrate, and on any new surfaces generated during growth, constitutesa growth sector. For example, in FIG. 3 diamond growth 24 arises fromthe {101} plane and thus is the {101} growth sector.

Competing with the homoepitaxial single crystal growth will bepolycrystalline diamond growth 20 which will take place on the surface12. Depending on the thickness of the single crystal diamond layerproduced on the surface 14, the polycrystalline diamond growth 20 maywell meet the homoepitaxial single crystal diamond growth along line 22,as illustrated in FIG. 3.

Based on FIG. 2, one might expect that the purely lateral growth on thesubstrate side surfaces could be used to fabricate a larger substrate,including the material of the original substrate. However, as is clearfrom FIG. 3, such a plate would actually contain competingpolycrystalline growth. A plate fabricated parallel to the originalsubstrate, but higher up in the grown layer is likely to containtwinning, especially from material in the {111} growth sector.

Under growth conditions where polycrystalline diamond does not competewith the single crystal diamond there still remains the problem that thequality of the lateral single crystal growth is generally poor, as aresult of the different geometry and process conditions present at thediamond substrate edges, exacerbated by the method used to suppresspolycrystalline growth.

Defects in the substrate used for CVD diamond growth replicate into thelayer grown thereon. Clearly, since the process is homoepitaxial,regions such as twins are continued in the new growth. In addition,structures such as dislocations are continued, since by its very naturea line dislocation cannot simply self terminate, and the probability oftwo opposite dislocations annihilating is very small. Each time a growthprocess is initiated, additional dislocations are formed, primarily atheterogeneities on the surface, which may be etch pits, dust particles,growth sector boundaries and the like. Dislocations are thus aparticular problem in single crystal CVD diamond substrates, and in aseries of growths in which the overgrowth from one process is used asthe substrate for the next, the density of dislocations tends toincrease substantially.

SUMMARY OF THE INVENTION

According to the present invention, a method of producing a plate ofsingle crystal diamond includes the steps of providing a diamondsubstrate having a surface substantially free of surface defects,growing diamond homoepitaxially on the surface by chemical vapourdeposition (CVD) and severing the homoepitaxial CVD grown diamond andthe substrate transverse, typically normal (that is, at or close to90°), to the surface of the substrate on which diamond growth took placeto produce a plate of single crystal CVD diamond.

The homoepitaxial CVD diamond growth on the surface of the substratepreferably takes place by the method described in WO 01/96634. Usingthis method, in particular, it is possible to grow thick, high puritysingle crystal diamond on a substrate. A growth thickness of thehomoepitaxial grown CVD diamond of greater than 10 mm, preferablygreater than 12 mm, and more preferably greater than 15 mm, can beachieved. Thus, it is possible, by the method of the invention, toproduce single crystal CVD diamond plates having at least one lineardimension exceeding 10 mm, preferably exceeding 12 mm and morepreferably exceeding 15 mm. By “linear dimension” is meant any linearmeasurement taken between two points on or adjacent to the majorsurfaces. For instance, such linear dimension may be the length of anedge of the substrate, a measurement from one edge, or a point on theedge, to another edge, or another point on the edge, an axis or otherlike measurement.

In particular, it is possible by the method of the invention to producerectangular (001) single crystal diamond plates which are bounded by{100} side surfaces or faces which have at least one linear dimension,such as a linear <100> edge dimension, exceeding 10 mm, preferablyexceeding 12 mm and more preferably exceeding 15 mm.

The plate of single crystal CVD diamond produced by the method may thenitself be used as a substrate in the method of the invention. Thicksingle CVD crystal diamond can be grown homoepitaxially on a majorsurface of the plate.

The invention provides, according to another aspect, a (001) singlecrystal CVD diamond plate having major surfaces on opposite sidesthereof bounded by {100} side surfaces, i.e. a plate in which the majorsurfaces are {001} faces, each major surface having at least one lineardimension exceeding 10 mm. In one form of the invention, the plate has arectangular, square, parallelogram or like shape, at least one of theside surfaces of which, and preferably both side surfaces, has adimension exceeding 10 mm, preferably exceeding 12 mm and morepreferably exceeding 15 mm. Most preferable is that these side surfacesare {100} surfaces or faces, such that the plate edge dimension (ordimensions) exceeding 10 mm is in the <100> direction. Further, themethod of the invention provides for a larger plate or piece of diamondfrom which such a plate bounded by {100} side surfaces and {001} majorsurfaces can be fabricated.

In the homoepitaxial diamond growth which occurs on the surface of thediamond substrate, any dislocations or defects in that surface, orarising at the interface with the substrate, or from the edges of thesubstrate, generally propagate vertically in the diamond growth. Thus,if the severing takes place substantially normal to the surface on whichdiamond growth took place, then the severed surface will havesubstantially no dislocations within the material intersecting thesurface, as they will be running generally parallel to the surface. Thusa reduction in the dislocation density in the volume of the material canbe achieved by repeating the method using this new plate as thesubstrate, and a resulting further reduction in the density ofdislocations cutting the major surface of any plates cut normal to thissubstrate. Furthermore, there are applications that benefit from platesin which the dislocations that are present run generally parallel to themajor faces rather than generally normal to them.

Generally the highest quality CVD growth is that contained within thevertical (001) growth sector. Furthermore, since the edges of thesubstrate can form dislocations and these generally rise verticallyupwards, then the highest quality volume of the CVD growth is thatbounded by the vertical planes rising up from the substrate edges. Themethod of this invention enables one or more new large area plates to befabricated from entirely within this volume, thus minimising the defectswithin the plate, and maximising its crystal quality.

Combining the various features of this invention, it is possible toproduce diamond with a lower dislocation density than the startingsubstrate material, with the lower limit on dislocation density set onlyby the number of times the method is to be repeated. In particular, thelarge area plate of the invention and any layers subsequentlysynthesised on it can have a dislocation density, typically intersectinga surface normal to the growth direction (this surface generally showingthe highest dislocation density in CVD diamond), which is less than50/mm², and preferably less than 20/mm², and more preferably less than10/mm² and even more preferably less than 5/mm². The defect density ismost easily characterised by optical evaluation after using a plasma orchemical etch optimised to reveal the defects (referred to as arevealing plasma etch), using for example a brief plasma etch of thetype described in WO 01/96634. In addition, for applications in whichthe dislocation density intersecting the major face of the plate is ofprimary concern, then a plate fabricated by the method of this inventioncan exhibit a dislocation density on its major face which is less than50/mm², and preferably less than 20/mm², and more preferably less than10/mm² and even more preferably less than 5/mm².

Where the substrate is a natural or HPHT synthetic substrate, it isgenerally not advantageous for the normally cut plate to include thematerial from the original substrate, although this can be done. It canbe advantageous to include material from the substrate in this platewhen the substrate is itself a CVD diamond plate, which may itself havebeen prepared by this method.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of a diamond plate on which idealhomoepitaxial diamond growth has taken place;

FIG. 2 is a section along the line 2-2 of FIG. 1;

FIG. 3 is a section through a diamond plate illustrating single crystaldiamond growth and polycrystalline diamond growth;

FIG. 4 is a section through a diamond plate on which homoepitaxialdiamond growth according to an embodiment of the invention has takenplace;

FIG. 5 is a schematic of a diamond plate showing the angle α of thedislocation direction relative to the major surfaces of the diamondplate; and

FIG. 6 is a schematic of a diamond plate showing the angle β of thedislocation direction relative to the normal to the major surfaces ofthe plate.

DESCRIPTION OF AN EMBODIMENT

An embodiment of the invention will now be described with reference tothe accompanying drawings. Referring to FIG. 4, a diamond plate 30 isprovided. The diamond plate 30 is a plate of single crystal diamond. Theupper face 32 is the (001) face and the side surfaces 34 are {010}faces. The surface 32 is substantially free of surface defects, moreparticularly substantially free of crystal defects as described in WO01/96634.

Following the method described in WO 01/96634, diamond growth 36 takesplace on the diamond substrate 30. This diamond growth occurs verticallyon the upper surface 32, outwards from the corners 38 of the substrate30 and outwards from the side surfaces 34. This diamond growth willgenerally be homoepitaxial, single crystal and of high quality, althoughdislocations and twinning on the {111} may be present as describedearlier.

Inevitably, some polycrystalline diamond growth will occur on thesurface on which the substrate is placed. This polycrystalline diamondgrowth may, depending on the thickness of the diamond growth region 36,meet the lower surface 40 of this region.

Once a desired thickness of diamond growth 36 has taken place, thediamond growth region 36 and substrate 30 are severed normal (atapproximately 90°) to the surface 32, as illustrated by dotted lines 44.This produces a plate 46 of high quality single crystal diamond. Theinterface between the original substrate and the diamond growth will,for practical purposes, be indistinguishable from the bulk of thesample. The original substrate material may form part of plate 46 or beremoved from it. More than one plate may be produced, with each plateparallel to the next and normal to the substrate.

Using the method of WO 01/96634, it is possible to produce a diamondgrowth region 36 which exceeds 10 mm in depth. Thus, the diamond plate46 which is produced will have side surfaces 48 which exceed 10 mm inlength.

The plate 46 may be used as a substrate for the method of the invention.Thus, if the plate 46 has side surfaces 48 greater than 10 mm in lengthand diamond growth exceeding 10 mm in thickness is produced on the majorsurface 50 of the plate, it is possible to produce a square, rectangularor similar shaped plate which has all four side surfaces exceeding 10 mmin length.

Severing in FIG. 4 is shown to take place perpendicular to the surface32. Severing can take place at angles other than perpendicular to thesurface 32, excluding plates which are parallel to the substrate. Platesproduced at angles other than normal to the substrate, where thesubstrate has a (001) major face, will have major faces other than the{100}, such as the {110}, {113}, {111} or higher order planes.

Further, it is possible to sever along planes which are at right anglesto the sever planes 44 of FIG. 4, which will also form a plate with amajor {100} face, or at any other angle relative to the sever planes 44,which will form plates with major faces of the type {hk0}. To achievesingle crystal diamond plates, some trimming of polycrystalline ordefective growth at the edges may be necessary.

Those skilled in the art will recognise that the general method need notbe restricted to substrates with a (001) major face, but could equallybe applied to other substrates with, for example, {110}, {113}, or even{111} major faces, but that in general the preferred method is to use asubstrate with a (001) major face, since the highest quality CVD diamondgrowth can be most easily grown on this face and the disposition offacets formed on the growing CVD on this face is generally mostappropriate for the production of large plates cut from the materialgrown.

For this reason, the key dimension in a substrate plate with a (001)major face is the largest rectangular plate which can be fabricatedbounded only by {100} side faces. Growth on this plate can relativelyeasily produce the plate bounded by {110} side surfaces or faces whichis rotated by 45°, as shown in FIG. 1, since this makes limited or nouse of {111} growth sector material. This new plate, bounded by {110}side faces has an area which is at least double that of the {100}bounded plate, but the original {100} bounded plate generally remainsthe largest inscribed {100} bounded plate which can be fabricated fromit. For this reason, reference to the size of a single crystal diamondplate with a (001) major face in this specification often explicitlyrefers to the size of the largest area inscribed rectangular platebounded by {100} edges, if the plate does not already have {100} edges.

Application of the method of this invention enables the manufacture ofproducts not previously possible. For instance, large area windows,where for reasons of clear aperture, support, mechanical integrity,vacuum integrity etc. an assembly of smaller windows will not suffice,are now possible. High voltage devices, where the large area providesthe protection from arcing round the active area of the device, are alsopossible. The low dislocation density material of the invention furtherenables applications such as electronic devices in which dislocationsact as charge carrier traps or electrical short circuits.

The growth direction of a CVD diamond layer can generally be determinedfrom the dislocation structures within it. There are a range ofconfigurations which can be present.

1) The simplest case is where the dislocations all grow largely paralleland in the direction of growth, making the growth direction clearlyevident.

2) Another common case is where the dislocations fan out slowly aboutthe growth direction, usually exhibiting some form of symmetry about thegrowth direction and at an angle typically less than 20°, and moretypically less than 15°, and even more typically less than 10°, and mosttypically less than 5° about this axis. Again from a small area of theCVD diamond layer the growth direction is easily determined from thedislocations.

3) On occasion, the growth face is not itself at right angles to thelocal growth direction, but at some small angle away from this. Undersuch circumstances the dislocations may be biased towards the directionnormal to the substrate surface of the growth zone in which they arefound. Particularly near edges, the growth direction may varysubstantially from the bulk of the layer, for example at {101} edgebevels on a substrate with a {001} major growth face. In both theseinstances, taken over the whole substrate the general growth directionis clearly evident from the dislocation structures, but equally evidentis that the material is formed from more than one growth sector. Inapplications in which the directions of the dislocations is ofimportance, then it is generally desirable to use material from only onegrowth sector.

For the purposes of this specification, the direction of thedislocations is that direction which an analysis of the dislocationdistribution would suggest to be the growth direction of the layer basedon the above models. Typically and preferably, the direction of thedislocations within a particular growth sector will then be the meandirection of the dislocations using a vector average, and with at least70%, more typically 80%, and even more typically 90% of the dislocationslying in a direction which is within 20°, more preferably 15°, even morepreferably 10° and most preferably 5° of the mean direction.

The direction of dislocations can be determined for example by X-raytopography. Such methods do not necessarily resolve individualdislocations but may resolve dislocation bundles, generally with anintensity in part proportional to the number of dislocations in thebundle. Simple or preferably intensity weighted vector averaging is thenpossible from topographs imaging cross sections in the plane of thedislocation direction, with a topograph taken normal to that directionbeing distinct in having a pattern of points rather than lines. Wherethe original growth direction of a plate is known, then this is asensible starting point from which to determine the dislocationdirection.

Having determined the dislocation direction according to the abovemethod, its orientation can be classified relative to the major faces ofthe single crystal CVD diamond plate. Referring to FIG. 5, a diamondplate 60 has opposite major surfaces 62 and 64. The direction of thedislocations, indicated generally by lines 66, is considered to beoriented generally parallel to the major faces 62,64 of the diamondplate 60 if the dislocations direction 66 makes an angle α of less than30°, preferably less than 20°, more preferably less than 15°, even morepreferably less than 10°, and most preferably less than 5° from a plane68,70 of at least one of the major faces 62,64 of the plate 60. Thisorientation of dislocations is typically achieved when the singlecrystal CVD diamond plate is severed substantially perpendicular to thesubstrate on which growth took place, in particular when severed fromthe highest quality CVD growth contained within the vertical (001)growth sector.

Applications benefiting from the dislocation direction lying generallyparallel to the major faces include optical applications where theeffect on the variation of refractive index observed across a light beampassing through the plate is to substantially reduce the spread,compared to that when the same dislocation distribution is substantiallynormal to the major surfaces. Such applications benefit from being ableto produce plates whose lateral dimensions both exceed 2 mm, morepreferably 3 mm, even more preferably 4 mm, even more preferably 5 mmand even more preferably 7 mm, as is now made possible by the method ofthis invention.

Further applications benefiting from selecting the direction of thedislocations to be generally parallel to the major faces of the plateare in applications using high voltage, where dislocations can provide ashort circuit in the direction of the applied voltage.

Another application is that of laser windows, where the effect of thebeam travelling parallel to the dislocations can enhance local electricfields and result in failure. This can be controlled by eitheroffsetting the dislocation direction from the beam direction, orpreferably setting the dislocation direction parallel to the major facesof the laser window and thus at right angles to the incident laser beam.Thus the maximum laser damage threshold can be achieved by practicingthe method of the invention.

Another way of classifying the dislocation direction is its orientationrelative to the normal to a major face of the plate. Referring to FIG.6, a diamond plate 80 has opposite major surfaces 82 and 84. Thedislocation direction 86 is considered to be offset away from the normal88 to at least one of the major faces 82,84 of the plate if the angle βbetween the dislocation direction 86, determined by the above method,and the normal 88 exceeds 20°, more preferably exceeds 30°, even morepreferably exceeds 40°, and most preferably exceeds 50°. Thisorientation of dislocations is typically achieved when the singlecrystal CVD diamond plate is severed at an angle to the surface of thesubstrate on which growth took place. Alternatively, it may occur wherethe plate is severed substantially perpendicular to the substrate onwhich growth took place, but in a region where the growth face itself isnot parallel to the original substrate surface, for instance in a {101}growth sector of a layer grown on a (001) substrate.

Substantial benefit can be achieved in certain applications by ensuringthe dislocation direction is merely offset away from the normal to atleast one of the major faces of the plate. Such requirements are foundin the application of diamond to etalons.

This invention may be further understood by way of the followingnon-limiting examples.

Example 1

Two {001} synthetic diamond substrates were prepared for CVD diamondgrowth according to the method described in WO 01/96633. A layer wasthen grown onto these diamond substrates to a thickness of 6.7 mm. Thelayers were characterised for their dislocation direction, and it wasfound that >90% of dislocations visible by X-ray topography were within20° of the growth direction, and >80% of the dislocations were within10° of the growth direction.

One plate was cut out of each of these layers such that the major facesof each plate had dimensions >6×5 mm and the direction of growth was inthe plane of the major faces.

One plate was then used for a second stage of CVD diamond growth,preparing it according to the method of WO 01/96633, thus producing asecond layer which was in excess of 4 mm thick and suitable for thepreparation of a 4×4 mm plate cut to include the growth direction in amajor face. This layer was then characterised for it dislocation densityin the direction of growth, by producing a small facet and using themethod of a revealing plasma etch, which found the dislocation densityto be very low and in the region of 10/mm². This made the materialparticularly suited to the application of etalons.

Example 2

In optical applications, a key parameter is the uniformity and spread invalues of properties such as birefringence and refractive index. Theseproperties are affected by the strain fields surrounding dislocationbundles.

Two {001} synthetic diamond substrates were prepared for CVD diamondgrowth according to the method described in WO 01/96633. A layer wasgrown onto this diamond to a thickness of 4 mm. The layers werecharacterised for dislocation direction and it was found that the meandislocation direction lay within 15° of the growth direction. Two plateswere cut out of these layers such that the major faces of the plates haddimensions >4×4 mm and the direction of growth was in the plane of themajor faces.

These layers were subsequently used for substrates in a second growthprocess. X-ray topography showed that the resulting growth (to athickness of 3.5 mm) had a very low dislocation content, and that thedislocations in the new overgrowth were perpendicular to those in theoriginal CVD layer used as the substrate. Subsequent to this secondgrowth the samples were used in an optical application which requiredvery low scatter and birefringence.

Example 3

A synthetic diamond substrate was prepared for CVD diamond growthaccording to the method described in WO 01/96633. A layer was then grownonto this diamond to a thickness of 7.4 mm. The synthesis conditionswere such that this layer was boron doped to a concentration, asmeasured in the solid, of 7×10¹⁶ [B] atoms/cm³. The layer wascharacterised for its dislocation direction, with the mean dislocationdirection found to be within 25° of the growth direction. Two plateswere cut out of this layer such that the major faces of the plates haddimensions >4×4 mm and the direction of growth was in the plane of themajor faces.

These plates, because of the low density of dislocations intersectingthe major surfaces in combination with the boron doping, had particularuse as substrates for electronic devices such as a diamond metalsemiconductor field effect transistor (MESFET).

Example 4

A 6×6 mm synthetic substrate 1b was prepared using the method describedin WO 01/96633 This substrate was then grown on in stages, typicallyadding about 3 mm of growth in each stage. At the end of each stage thelayer was retained in the polycrystalline diamond layer that had grownaround it, this polycrystalline layer being trimmed to a disc about 25mm diameter using laser trimming, and then this disc mounted into arecessed tungsten or other metal disc such that the point where thesingle crystal was exposed above the polycrystalline diamond layer wasapproximately level (to within 0.3 mm) of the upper surface of thetungsten disc.

Using the above technique it was possible to grow layers with a finalthickness in the range 10-18 mm, from which plates with {100} edgescould be vertically cut. Plates were produced with a first <100>dimension in the plane of the plate of 10-16 mm, and a second orthogonaldimension of 3-8 mm.

These plates were then prepared as substrates and used for a secondstage of growth, again using the above technique, to produce layerswhich were 10-18 mm thick. From these layers it was possible to cutvertical plates which were greater than 10-18 mm in the <100> seconddimension within the major face and retaining the first <100> dimensionin the range 10-18 mm. For example, plates were produced which werelarger than 15 mm×12 mm, the dimensions being measured in orthogonal<100> directions.

What is claimed is:
 1. A (001) single crystal CVD diamond plate havingmajor surfaces on opposite sides thereof bounded by {100} side surfaces,each major surface having at least one linear dimension exceeding 10 mm.2. A diamond plate according to claim 1, wherein at least one lineardimension exceeds 12 mm.
 3. A diamond plate according to claim 2,wherein at least one linear dimension exceeds 15 mm.
 4. A diamond plateaccording to claim 1, having first and second linear dimensionsexceeding 10 mm.
 5. A diamond plate according to claim 4, wherein thefirst and/or the second linear dimension exceeds 12 mm.
 6. A diamondplate according to claim 5, wherein the first and/or the second lineardimension exceeds 15 mm.
 7. A diamond plate according to claim 1, whichis a rectangular (001) single crystal diamond plate bounded by {100}side surfaces, wherein the at least one linear dimension is an axis,lateral dimension or lateral edge dimension.
 8. A diamond plateaccording to claim 1, wherein the at least one linear dimension is a<100> edge formed by the intersection of a {100} side surface with amajor surface.
 9. A diamond plate according to claim 4, wherein thefirst and second linear dimensions are orthogonal <100> edges formed bythe intersection of respective {100} side surfaces with a major surface.10. A diamond plate according to claim 1, which has a rectangular,square, parallelogram or like shape.
 11. A single crystal CVD diamondplate having major surfaces on opposite sides thereof, and havingdislocations intersecting the major surfaces, wherein the density of thedislocations intersecting the major surfaces does not exceed 50/mm². 12.A diamond plate according to claim 11, wherein the density of thedislocations intersecting the major surfaces does not exceed 20/mm². 13.A diamond plate according to claim 12, wherein the density of thedislocations intersecting the major surfaces does not exceed 10/mm². 14.A diamond plate according to claim 13, wherein the density of thedislocations intersecting the major surfaces does not exceed 5/mm². 15.A diamond plate according to claim 11, wherein the density ofdislocations intersecting any other plane in the diamond plate does notexceed the respective density limit of the dislocations intersecting themajor surfaces.
 16. A diamond plate according to claim 11, wherein atleast one linear dimension exceeds 10 mm.
 17. A single crystal CVDdiamond plate, having major surfaces on opposite sides thereof, andhaving dislocations produced during growth, wherein the dislocations areoriented in a direction generally parallel to at least one of the majorsurfaces.
 18. A diamond plate according to claim 17, wherein thedirection of the dislocations is at an angle of less than 30° relativeto at least one of the major surfaces.
 19. A diamond plate according toclaim 18, wherein the direction of the dislocations is at an angle ofless than 20° relative to at least one of the major surfaces.
 20. Adiamond plate according to claim 19, wherein the direction of thedislocations is at an angle of less than 10° relative to at least one ofthe major surfaces.
 21. A diamond plate according to claim 20, whereinthe direction of the dislocations is at an angle of less than 5°relative to at least one of the major surfaces.
 22. A diamond plateaccording to claim 17, wherein each major surface has a first lineardimension, corresponding in direction to the general direction of thedislocations, exceeding 2 mm.
 23. A diamond plate according to claim 22,wherein the first linear dimension exceeds 3 mm.
 24. A diamond plateaccording to claim 23, wherein the first linear dimension exceeds 4 mm.25. A diamond plate according to claim 24, wherein the first lineardimension exceeds 5 mm.
 26. A diamond plate according to claim 25,wherein the first linear dimension exceeds 7 mm.
 27. A diamond plateaccording to claim 22, wherein a second linear dimension of each majorface orthogonal to the first linear dimension is equal to or greaterthan the first linear dimension.
 28. A single crystal CVD diamond plate,having major surfaces on opposite sides thereof, and having dislocationsproduced during growth, wherein the mean dislocation direction isoriented in a direction offset from the normal to at least one of themajor surfaces.
 29. A diamond plate according to claim 28, wherein themean dislocation direction is offset from the normal to at least one ofthe major surfaces by an angle exceeding 20°.
 30. A diamond plateaccording to claim 29, wherein the mean dislocation direction is offsetfrom the normal to at least one of the major surfaces by an angleexceeding 30°.
 31. A diamond plate according to claim 30, wherein themean dislocation direction is offset from the normal to at least one ofthe major surfaces by an angle exceeding 40°.
 32. A diamond plateaccording to claim 31, wherein the mean dislocation direction is offsetfrom the normal to at least one of the major surfaces by an angleexceeding 50°.